High-frequency electromagnetic waves are generated in connection with the switching action of semiconductor devices that constitute an LSI (large-scale integrated circuit) or an IC (integrated circuit), and part of the generated high-frequency electromagnetic waves leaks to a power supply distribution circuit of a printed circuit board via a power supply interconnection, a package, etc. When high-frequency electromagnetic waves are inductively coupled to a signal interconnection and the like within an LSI, a package and a substrate of a printed circuit board in the process of their propagation in the power supply interconnection, high-frequency electromagnetic waves leak from signal cables and equipment. Also, when the surge impedance of a power supply interconnection as viewed from switching components within an LSI is large, high-frequency electromagnetic waves generated in the switching components within the LSI cause interference in a signal interconnection, thereby generating signal voltage strains. Also, these high-frequency electromagnetic waves induce variations in the power supply voltage of the switching components. In order to suppress such electromagnetic interference, it is effective to insert a power supply decoupling circuit in which the insertion position and decoupling characteristics are considered so that the electromagnetic interference with the power supply interconnection from the LSI to the printed wiring board becomes minimized.
Conventionally, in semiconductor devices, as described in the Japanese Patent Laid-Open No. 10-2706643, decoupling has been performed by adding capacitors, which are handled as lumped components because of the small component size relative to a wavelength corresponding to the working frequency of a circuit.
When capacitors are used, it is necessary to consider also the series inductance components of the connection wiring part, and in this case, decoupling capacitors exhibit inductance characteristics at frequencies of not less than the series resonance frequency of capacitance and inductance, with the result that the higher the frequency, the more impedance will increase, thereby leading to the deterioration of decoupling characteristics.
As a measure against this phenomenon, there has been adopted a technique by which capacitors are disposed in a divided manner within an LSI or an IC, a package and a printed wiring board. However, also in this case, it is impossible to ignore the inductance of an interconnection which connects capacitors and a power supply distribution line together and hence in bands in which the working frequency is not less than several hundreds of megahertz, there has been a limit to changing the impedance of a decoupling circuit from inductance characteristics to capacitive characteristics.